Developer powder applicator unit having a supply roll with a magnetized working surface



Jan. 9, 1968 D. F. ANDERSON ETAL 3,362,380

' DEVELOPER POWDER APPLICATOR UNIT HAVING A SUPPLY ROLL WITH AMAGNETIZED WORKING SURFACE Filed Oct. 8, 1964 United States Patent GDEVELOPER POWDER APPLICATGR UNIT HAV- ING A SUPPLY ROLL WITH AMAGNETIZED WORKKNG SURFACE Donald F. Anderson, St. Anthony Village, andBryce L. Clark, St. Paul, Minn, assignors to Minnesota Mining andManufacturing, St. Paul, Minn., a corporation of Delaware Filed on. s,1964, Ser. No. 402,389 1 Claim. or. 118-620 This invention relates tocopying machines useful in the copying of printed documents and similargraphic originals by methods involving formation of an invisible latentimage followed by powder developing of a corresponding permanent visibleimage. More particularly, the present invention relates to a powderdeveloper module, one important modification being specifically adaptedfor use in conjunction with a popular form of thermographic copyingmachine and employing cooperating copy-papers and developer powders aswill hereinafter appear.

Developer powders for developing visible images from electrostatic orother latent images ordinarily consist of colored electroscopic powdersin conjunction with much larger particles of glass or other carriermedia. In some instances magnetic materials serve as the carrier and arethemselves oriented in the form of magnetic brushes attached topermanently magnetized handle members. In all cases the loose mass ofpowder is slid or drawn over the imaged surface to leave a portion ofthe powder at the image-forming areas.

The present invention introduces a new and improved technique of powderapplication, which while not restricted thereto, is particularly usefulin the developing of permanent visible images from latent images formedby application of a corresponding heat pattern to copy-sheets coatedwith a hard solid fusible material which fuses to a metastable liquidwhen heated. A magnetic powder is retained on a magnetic bed as a smoothfirm surface coating with which the sheet having the latent image isthen placed in momentary sliding contact. The powder is wetted andpreferentially retained by the metastable liquid which thereafter soonsolidifies. Any traces of loose powder remaining on the sheet areremoved by brushing with a soft brush, which in the automatic developerhere to be described further serves to eject the copy.

A suitable magnetic powder may consist of Mapico Black magnetic ironoxide uniformly dispersed in an equal weight of molten benzil, thecooled and hardened mixture being reduced to fine particle size. Thebenzil serves as a thermoplastic binder for the magnetic particles.Additional coloring agents, e.g. carbon black or organic dyes, may beincluded if desired.

In the drawing,

FIGURE 1 is a side elevation, taken along section 11 of FIGURE 2, of anillustrative developing device in association with related components ofa commercial thermographic copying machine;

FIGURE 2 is a partial plan view corresponding to FIGURE 1, with partscut away as indicated;

FIGURE 3 is a partial plan view showing a portion of thepowder-retaining trough and guide members;

FIGURE 4 is a fragmentary representation in perspective of the structureof FIGURE 3; and

FIGURE 5 is a representation of the surface arrangement of the roll 12of FIGURES 1 and 2.

The device as illustrated consistis essentially of guide members and 11,powder distribution roll 12, trough 13, feed roll 14-, ejector roll 15,and guide members 16 and 17 forming parts of an enclosing frame 18. Alsoshown in FIGURES 1 and 2 are print roll 21}, lamp assembly 21, guideroll 22, drive roll 23, belt 24, and guide ice members 25 and 26 of thethermographic copying machine, in this instance a Thermo-Fax copyingmachine as described in Kuhrmeyer et al. U.S. Patent No. 2,891,165.

The paper guide members 10 and 11 may form a part of the thermographiccopying machine but are modified as shown in FIGURE 1. The lower guidemember 11 has upturned bottom edge closely aligned with the extendedsurface of the roll 12 for directing the copy into tangential contactwith the latter. The guide 10 has a smooth straight lower edge closelyadjacent the tip of the guide 11 and the surface of the roll 12, for apurpose later to be described.

The entire surface of the roll 12 is provided with a uniform pattern ofalternating closely spaced magnetic poles. Typically, a non-magneticroll is covered with small Alnico or equivalent bar magnets closelyspaced together in rows as illustrated in greater detail in FIGURE 5.Each magnet is approximately /2" long, 7 Wide and /8" thick, adjacentmagnetic poles being arranged in opposition. The roll is made ofaluminum. It is about 4;" in diameter and 8 /2 long, and supports atotal of uniforrnly spaced magnets, in ten rows of alternately 12 and 13magnets, the over-all diameter thus being about 1%. The magnets arebonded to the aluminum surface with a strong elastomeric adhesive.

The structure described is convenient to assemble and provides a highstrength magnetic field having uniformly spaced small separate zones ofhigh field gradient, in this case with opposing polarity. Anothersuitable structure but having zones of identical rather than oppositepolarity is formed by inserting the small bar magnets length wise intoradially extending openings in the non-magnetic roll surface with likepoles at the surface, again to obtain uniformly spaced small separatezones of high field gradient.

The trough 13 in which the roll 12 rotates contains a magnetic developerpowder 27 which is taken up by the magnetic surface of the roll andleveled by a blade 28 formed of the in-turned edge of the sheet materialforming the trough. As the roll 12 is rotated past the blade 28, itattracts and maintains a smooth continuous and compact powder surfacecoating, the diameter being maintained at just over 1% inches. Thespecific dimensions given are not critical but will serve to indicatethe type of surface and the manner in which it is obtained.

At the side of the trough 13 opposite the blade 28 there is provided aseries of thin guide plates 29 uniformly spaced along supporting rods 30and supporting at their forward tips a smoothing bar 31. The bar 31 andthe rounded upper edges of the plates 29 lie beneath the feed roll 14for directing the composite against the roll 15.

The soft surface of the ejector roll 15 contacts the feed roll 14 andserves as a portion of the ejector chute otherwise defined by guidemembers 16 and 17.

The rolls 12, 14 and 15 are positively driven, e.g. by suitable geartrain, and preferably but not necessarily from the same source of poweremployed in rotating the drive roll 23 of the copying machine. Thesurface speed of the feed roll 14 is the same as that of the belt 24 androlls 20, 22 and 23, whereas roll 12 is driven at approximately threetimes, and roll 15 at approximately five times that surface speed.

The production of copies proceeds as follows. A couplet or composite ofa graphic original 32 and copy-sheet 33, each with the print surfaceupward, is fed into the machine between guide members 25 and 26, andpasses around roll 20, beneath belt 24, and past the focus of lampassembly 21. The radiation from the lamp produces a heat patterncorresponding to the differentially radiation-absorptive printed indiciaon the graphic original. Conduction of the heat pattern to thecopy-sheet 33 fuses a the corresponding areas of the coating on thatsheet and reduces the coating to a metastable liquid. The compositeadvances between the guides 10 and 11, the latter directing the forwardedge of the two sheets into tangency with the comparatively rapidlyadvancing surface of the powder distribution roll 12, and thereafteragainst the surface of the feed roll 14. The sheets continue across theroll 12, past the upper surface of the smoothing bar 31, and intocontact with the surface of the roll 14. The latter re-directs thecomposite across the upper edges of the plates 29, against the roll 15,and into the nip between rolls 14 and 15. From there the composite isdirected between guide members 16 and 17 and from the machine, where thecompleted copy is separated from the original.

As the trailing edge of the composite reaches the lower edge of theguide 10, the rapid rotation of the powder distribution roll 12 has atendency to force powder from the surface of the roll between the edgesof the two sheets. This tendency is overcome by the snap action of thetwo stiff, resiliently fiexible, paper sheets immediately the trailingedge has passed the lower edge of the guide, as induced by the positionof the bar 31 somewhat above the line connecting the upper surface ofroll 12 and the lower surface of roll 14, i.e. toward the feed roll fromthe interconnecting plane of tangency. By this action the two sheets arelifted above and out of contact with the stirface of the roll 12 duringthe critical terminal period of their travel past the developing area.

The feed roll 14, operating at the surface speed of the thermographiccopying machine, is composed of extremely soft and resilient urethanefoam or sponge, which exerts against the contacting sheet material amild pulling action just sufiicient to cause the sheets to advance whenunder light restraining tension. Increased drive is provided by thecooperative effects of the two rolls 14 and 15, the latter also servingto remove from the powdered copy-sheet surface any small traces of loosepowder which may remain. Roll 15 for this purpose consists of a hardsupporting roll having a soft fibrous surface covering 34, for exampleof sheepskin. Some of the loose powder may remain adhered to the fibroussurface, but much of it is detached and remains within and on the bottomof the frame 18 which may periodically be detached for cleaning. Inpractice it is found that very little of the magnetic powder is removedfrom the magnetic surface of the drum 12 other than the portion which ispermanently retained at the image areas of the copy-sheet, any loosenedpowder being magnetically attracted to the surface of the powder supplyroll 12.

What is claimed is as follows:

1. A powder applicator unit comprising: an open trough-like receptaclefor magnetic developer powder; a scraper bar along the forward edge ofsaid open receptacle; a powder supply roll having a magnetized workingsurface having a pattern of uniformly spaced small separate zones ofhigh field gradient and capable of attracting and retaining a thickdeposit of a magnetic dcveloper powder, said roll dipping into saidreceptacle and rotatable with its surface in close uniform proximity tosaid scraper bar; a soft compressible feed roll parallel to said supplyroll and above the rearward edge of said receptacle; a smoothing barbetween said supply roll and said feed roll and with its free smoothingsurface disposed toward said feed roll from the interconnecting plane oftangency between the said rolls; a plurality of narrow guide platesclosely spaced from said feed roll and extending from said smoothingbar; and a soft fibrous-surfaced ejector roll parallel to and in lightsurface contact with said feed roll and beyond said guide plates; saidsupply roll, feed roll, and ejector roll being interconnected forpositive rotation at relative surface speeds of approximately three, oneand five respectively and in a direction for urging a copy-sheet throughsaid unit from said sup ly roll to said ejector roll.

References Cited UNITED STATES PATENTS 3,146,100 8/1964 Kaufman 951.7 X3,260,612 7/1966 Dulmage et al. 25065 X WILLIAM F. LINDQUIST, PrimaryExaminer. RALPH G. NILSON, Examiner.

1. A POWDER APPLICATOR UNIT CORRESPONDING: AN OPEN TROUGH-LIKERECEPTACLE FOR MAGNETIC DEVLOPER POWDER; A SCRAPER BAR ALONG THE FORWARDEDGE OF SAID OPEN RECEPTACLE; A POWDER SUPPLY ROLL HAVING A MAGNETIZEDWORKING SURFACE HAVING A PATTERN OF UNIFORMLY SPACED SMALL SEPARATEDZONES OF HIGH FIELD GRADIENT AND CAPABLE OF ATTRACTING AND RETAINING ATHICK DEPOSIT OF A MAGNETIC DEVELOPER POWDER, AND ROLL DIPPING INTO SAIDRECEPTACLE AND ROTATABLE WITH ITS SURFACE IN CLOSE UNIFORM PROXIMITY TOSAID SCRAPER BAR; A SOFT COMPRESSIBLE FEED ROLL PARALLEL TO SAID SUPPLYROLL AND ABOVE THE REARWARD EDGE OF SAID RECEPTACLE; A SMOOTHING BARBETWEEN SAID SUPPLY ROLL AND SAID FEED ROLL AND WITH ITS FREE SMOOTHINGSURFACE DISPOSED TOWARD SAID FEED ROLL FROM THE INTERCONNECTING PLANE OFTANGENCY BETWEEN THE SAID ROLLS; A PLURALITY OF NARROW GUIDE PLATESCLOSELY SPACED FROM SAID FEED ROOL AND EXTENDING FROM SAID SMOOTHINGBAR; AND A SOFT FIBROUS-SURFACED EJECTOR ROLL PARALLEL TO AND IN LIGHTSURFACE CONTACT WITH SAID, FEED ROLL, AND EJECTOR ROLL BEINGINTERCONNECTED FOR ROLL, FEED ROLL, AND EJECTOR ROLL BEINGINTERCONNECTED FOR POSITIVE ROTATION AT RELATIVE SURFACE SPEEDS OFAPPROXIMATELY THREE, ONE AND FIVE RESPECTIVELY AND IN A DIRECTION FORURGING A COPY-SHEET THROUGH SAID UNIT FROM SAID SUPPLY ROLL TO SAIDEJECTOR ROLL.